Fusible electric circuit protector



Sept.A 19, 17944. 'M B, woon 2,358,676

FUSIBLE` ELECTRIC CIRCUIT PROTECTOR Filed Sept. 7,- 1939 Patented Sept. 19, 1944 FUSIBLE ELECTRIC CIRCUIT PROTECTOR Morris B. Wood, Newbury, Mass., assigner to The Chase Shawmut Company,

Newburyport,

Mass., a corporation of Massachusetts Application September 7, 1939, Serial No. 293,767

13 Claims.

This invention relates to fusible electric circuit protective devices of the type having a readily fusible metal which electrically connects separable elements of a circuit conductor and is adapted to be melted or softened by the electrically generated heating of a part of the conductor to release its hold upon the separable elements to effect circuit interruption. Such a heating conductor usually includes a fuse adapted to interrupt the circuit more quickly than the fusible metal when traversed by high currents.

The present invention relates particularly although not restricted to a cartridge type of protective device wherein the fusible interrupting element and a supplementary heating element are enclosed within a tubular casing having suitable end terminals.

In devices of the type above referred to it is desirable to employ a spring which serves to effect separation of the cooperating circuit interrupting elements upon fusing of the fusible metal.

When a thermal -cut-out device of the above type is used to interrupt circuits traversed by currents of considerable magnitude, the circuit interrup-ting arc may be quite severe especially on currents approximating a short-circuit in value. It is, accordingly, desirable to surround the circuit interrupting elements of the device with some arc quenching powdered or granular materialy such as is customary to use in nonrenewable cartridge fuses. 'I'he use of such material about and in contact with the circuit interrupting spring, however, would interfere with the free operation of the spring.

One object of the present invention, accordingly, is to provide an improved construction wherein the fusible interrupting element is surrounded by an are quenching powdered or granular material and in which the spring member for separating the fused ends of the fusible link is located in a chamber in such a manner that the powdered or granular material cannot come into contact with the spring and thereby interfere with its free operation. As illustrated, the present invention'con-templates the use of a cartridge type Aof fuse having a plurality of chambers therein, in one of which the fusible interrupting element, or the fusing portion thereof, is located and surrounded by a granular or powdered arc quenching material.

A still further object of the invention is to provide a fusible electrical protective device wherein a fused end of the fusible interrupting device may be moved through .an opening in a partition member to quench or interrupt the arcupon fusing of the fusible interrupting element or upon fusing of the readily fusible means connecting the end of the fusible interrupting element with the heater element.

Since the fusible link of the device is surrounded by an arc quenching filler it is an object of this invention to obtain circuit interruption on low overload by moving the softened fusible mass, and preferably also the heater therefor, away from the fusible link.

A yet further object of the invention is generally to improve the construction and operation of thermally responsive electrical protective dev1ces.

With the above and other objects and features in view, the invention will now be described with reference to the accompanying drawing in which;

Fig. 1 is a longitudinal section through a cartridge type electrical protective device embodying the present invention;

Fig. 2 is a view similar to Fig. 1 but illustrating the operated position of the parts upon fusing of the fusible interrupting element;

Fig. 3 is a view similar to Figs. 1 and 2 but showing the operated position of the parts after the fusing of the fusible means connecting the fusible interrupting element and the heater element; and l Fig. 4 is a view in side elevation showing the relation of the parts before they are assembled within the casing.

The cartridge type thermal (protective device embodying the present invention includes a tubular insulating casing I0 having metal end caps I2 and I4 thereon which, as illustrated, are permanently fixed to the ends of the casing and constitute the circuit terminals of the device. The end caps are connected within the casing by an electrical conductor consisting of a fusible interrupting element or link l 6, a heater element I8, and a exible conductor 20.

The elements I6, I8 and 20 are assembled and connected together before they are inserted in the casing I0. The heater element I8, which is formed of suitable resistance metal, the characteristics of which depend upon the current to be carried by the device, is wound into the form of a close helical coil having a diameter slightly less than the inside diameter of the tubular casing I0. The fusible element or link I6 is formed of copper, Zinc, or other material having the proper thermal and electrical 'characteristics for the current to be handled. The link I6 is provided with a fusing section 22 of reduced crosssectional area which is adapted to fuse to interrupt the circuit when traversed by high overload currents such as those approximating a shortcircuit in value.

One end of the fusible link I6 is secured to one end of the coiled heating element I8 by a mass of low melting temperature solder 24, preferably contained within and adherent to the end lconvolution of the coil. The other end of the coiled heating element I8 is secured to one end of the flexible conductor 20 by a mass of high melting temperature solder 26. Y disc 28 of bre or other insulating material, having an opening 30 of an area slightly greater than the cross-sectional area of the fusible link I6 and a diameter slightly smaller than the internal diameter of the casing I0, is threaded on the link I6. A coiled spring 32 having a diameter substantially less than the inside diameter of the casing is then threaded on the fusible link Iand bears at one end on the disc 28. A second partition member or disc 34 of nbre or other insulating material, having an opening 36 slightly larger than the cross-sectional dimensions of the link, is then threaded on the link I6. The parts of the device thus assembled into a unit are shown in Fig. 4.

The end cap I4 is then soldered to the flexible conductor 2B by high melting temperature solder. The length of the flexible conductor between the end cap i4 and the end of the heating element I8 is of such length that the conductor 20 is slack or is not placed under tension whenV the parts are in completely assembled position within the casing Ill, as shown in Fig. 1. VThe unit is then inserted in the casing l and the end cap I4 is secured in position on the casing. The distance from the outer face of the disc 34 to the opposite endof the heating coil I8 with the spring 22 freely expanded is somewhat greater than the distance between the inner face of the end cap i4 and an internally projectingannular rib 3l formed in the casing IIl. Thus when the end cap I4 is secured in position, the spring 32 is, somewhat compressed thereby causing the disc or partition member 34 to seat firmly against the inwardly extending rib 31, thus effectively sealing the right hand end of the casing Hl.

The fuse link I6 is made long enough initially so that when the parts Yare in this position, the end of the fuse link will project materially beyond the open end of the casing which is later to be yclosed by the end cap I2. The open ended chamber 38, within which the fuse link I6 yis located, is then filled with a mass 40 of loose particles of arc quenching material of any usual or suitablercharacter which surrounds and is in intimate association with the fusible link I. Thel free end of the fuse link I6 is then inserted through an opening formed in the end cap I2 and the end icap is placed over and seated upon the end of the casing I El. The free end of the link is then pulled toward the left as viewed in Fig.` l until the spring 32V is compressed and the iparts occupy the position vwithin the casingV shown in Fig; 1. The fuse link is then bent over at substantially right angles and high melting temperature solder is used to secure the fuse link to ythe end capi I2 which thus maintains the fuse link I6 .under tension and the spring 32 under compression. vThe parts of the device are now completely assembled.

The fusible protective device thus constructed is operative to interrupt the circuit by fusing `of the fusible link I6 by currents of a magnitude A ipartition member orV approximating a short-circuit in value and the fusible mass 24 is so arranged that it will be heated to a fusing point by relatively long continued overload currents. Thus when the current is interrupted by fusing of the fusible link I6, the compressed spring 32 -is no longer restrained from expansion so that it moves the partition member 28 and the heating element I8 and the right hand end of the fusible link I6 toward the right into the position shown in Fig. 2, thus separating the fused end of the fusible link I6 and at the same time drawing one of the fused ends through the opening 36 in the rpartition member 34. The arc created by the fusing of the fuse link I6 is quenched by the action of the granular mass of arc quenching material 40. Any arc present at the time the fused end 42 of the link I6 passes through the slot or aperture 36 tends to be quenched by the deionizing action of the slot Vwalls and by theaction of the arc gases in expanding into the relatively low pressure right hand part of the casing.

If, on the other hand, a substantial overload current is continued for a relatively long period of time, the mass 24 of low melting temperature solder will fuse which will release the heating element I 8 from the rightV hand end of the fusible link I6. The spring 32 is no longer restrained from expansion and moves the heating element toward the right into the position shown in Fig. 3. The end of the fuse link I6 and the heating element I8 are thus relatively lWidely separated. When the right hand endV of the fuse link I6 is withdrawn from the heating element I8, an arc is oftentimes formed. The archowev'er, is drawn through the aperture 30 in the partition member 28 which tends to deionize the arc. a

It is evident that the above device operates equally effectively upon currents of greater magnitude approximatingla short-circuit in valueA or upon long continued relatively high overload currents. By the use of vthis construction, arcing is reduced to a minimum. Having thus describedmy invention, what I claim'as new and desire to secure by Letters Patent of the United States is.'

1. A fusibleV electrical protective device having, in combination, an enclosing casing, a. conductor within said casing comprising a fusible interrupting element and a heater element, fusible means receiving heat from said heater Yelement for directly connecting said fusible element and said heater element operable vwhen fused to permit separation of saidelements, partition members within said casing each having openings therein for receiving said fusible element, and means within the casing for effecting relative movement between the fusible element and the partition members to cause the circuit interrupting arc to be drawn through a saidopening in a partition member uponfusing of said fusible element and also uponthe fusing of said fusible connecting means.

`2. A fusible electrical protective devicev having, in combination, an enclosing casing, a conductor within said casing comprising a fusible interrupting element and a heater element, fusible means connecting said fusible element and said heater element operable when fused-by the heater element to permit separation of said elements, partition members within the casing havingopenings thereinfor receivingsaid fusible element, and means interposed between said partition members for moving the freed. end of said fusible interrupting element and a said partition member relatively to draw the circuit interrupting arc through a said'opening in a partition member upon fusing of said fusible interrupting element and also of said fusible connecting means.

3. A fusible electrical protective device having, in combination, an enclosing casing, end terminals on the casing, a conductor within the casingY connected to the terminals, said conductor comprising a fusible interrupting element and a heater element, means connecting the adjoining ends of said fusible and heater elements operable when fused to permit separation of said elements, spaced discs within the casing each having an opening for receiving the fusible element, and means for moving one of the discs in direction away from the fusible element upon fusing of the fusible element and also of the fusible connecting means to cause the circuit-interrupting arc to be drawn through the opening in one of the discs to interrupt the arc.

4. A fusible electrical protective device having, in combination, an enclosing casing, end terminals on said casing, a flexible conductor secured to one of the terminals, a heater element secured to the free end of the flexible conductor, a fusible interrupting element connected to the other end of the heater element, fusible means connecting the fusible element and the heating element operable when fused by the heating element to permit separation of the elements, a partition member within the casing located adjacent to the adjoining ends of said fusible element and said heater element, and means for effecting relative movement of the partition member and the fusible interrupting element to withdraw the end of the fusible interrupting element through an opening formed in the partition member upon fusing of said fusible connecting means.

5. A fusible electrical protective device having, in combination, an enclosing casing, end terminals on the casing, a conductor within the casing comprising a fusible interrupting element, a heater element and a flexible conductor connected at its free end to one of the end terminals, readily fusible means connecting the adjoining ends of the heater element and the fusible element operable vupon fusing to permit separation of the fusible element and the heater element, partition members within the casing each having an opening therein for receiving the fusible element, one of said partition members being located adjacent to the end of the fusible element connected to the heater element, the other partition member engaging an internal rib formed in said enclosing casing, spring means interposed between the partition members and arranged to effect separation of the fusible element and the heater element upon fusing of the fusible connecting means to Withdraw the end of the fusible element through the partition member located adjacent to the end of the fusible element to interrupt the arc, and means for connecting the other end of the fusible element to the end terminal to compress the spring interposed between the partition members.

6. A fusible electrical protective device having, in combination, an enclosing casing, and terminals on the casing, an electrical conductor within the casing including a fusible link and a movable heater element, a fusible mass connecting the fusible link and the heater element operable upon fusing to permit separation of the link and heater element, a flexible conductor connecting the free end of the heater element to onel of the end caps, an abutment member within said casing, and a spring interposed between said abutment member and said heater element maintained under tension by said fusible link and responsive to the fusing of said link and also said fusible mass to effect electrical separation of said link and said heater element by moving said heater element in a direction away from said fusible link.

7. A fusible protective device for electrical circuits having, in combination, an insulated casing, metallic end caps, a heating element connected to one of the end caps, a fusible link, a fusible mass connecting said fusible link and said heater element operable upon fusing to permit separation of the fusible link and the heater element, the other end of the fusible link being connected to the other of said end caps, an inwardly extending projection in the casing, a movable partition member on said link adjacent to said heater element, a second partition member on said link arranged to be seated against said inwardly extending projection, and a spring interposed between the partition members arranged to be placed under compression by the fuse link whereby the heater element is moved in a direction away from the fusible link upon fusing of either the fusible link or fusible mass.

8. A fusible protective device for electrical circuits having, in combination, an insulated casing, metallic end caps, a heating element connected to one of the end caps, a fusible link, a fusible mass connecting said fusible link and said heater element operable upon fusing to permit separation of the fusible link and the heater element, the other end of the fusible link being connected to the other of said end caps, an inwardly extending projecton in the casing, a partition member on said link adjacent to said heater element, a second partition member on said link arranged to be seated against said inwardly extending projection, and means interposed between the partition members effective upon separation of the fusible link and heater element to move the heater element away from the fused end of the fuse link and to cause an end of the fuse link which is freed by a fusing of the protective device to move relatively to a said partition member and through a said partition member.

9. A fusible electrical protective device having an enclosing casing having a partition separating said casing into two sections, an arc quenching filler in one section only, a fusible conductor mainly in said one section having an end part extended through an aperture in said partition, a heater in the other section, a fusible mass connecting said conductor end part and heater, and means responsive to the fusing of said fusible conductor to move said heater and draw said fused end part through said aperture into said other section.

10. A fusible electrical protective device having a casing provided with a partition having a small aperture, a fusible link in said casing extending through the aperture in said partition, a heating conductor, a fusible mass for connecting the link and the heating conductor, and means responsive to the fusing of said fusible mass to effect passage of an end part of said link through said small aperture.

11. A fusible electrical protective device cornprising an enclosing casing having an internal ledge intermediate its ends, a partition plate loose in said casing, a spring bearing against said plate in a direction to press it against said ledge, a fuse link in said casing having a fusing section on one side ofsaid plate, an end part of said link being extended loosely through said plate, a heater loose in `said casing on the other side of said plate, a fusible mass connecting said heater and end part of said link, said spring exerting pressure on said heater in a direction to move it away from said link, andV terminals connected to said link and heater.

12. A fusible element for a fusible electric circuit protector comprising a fusible link, a heater, an anchorage for one end part of said link, a fusible mass connecting the other end part ofsaid link with said heater, said! heater being other- Wise free for movement, a compression spring surrounding said link, and insulating plates loose on said link at opposite sides of said spring and pressed in opposite directions by said spring.

13. A fusible electrical protective device com- Y responsive to the fusing of said fusible mass for separating said conductors through said apertured means, one of said conductors being a fusible link adapted to fuse intermediate its ends prior to the fusing of said fusible mass `when traversed by a sufficiently heavy current, said apertured means also being close to the fusing region of said fusible link, said means responsive to the fusing of said fusible mass being also responsive to the fusing of said link for separating the fused ends of said link through said apertured means. f

MORRIS B. WOOD. 

